Essentials of Genetics William S. Klug 8th Edition Test Bank

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Essentials of Genetics William S. Klug 8th Edition Test Bank

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Essentials of Genetics, 8e (Klug)
Chapter 5 Sex Determination and Sex Chromosomes

1) The Protenor mode of sex determination is the ________.
A) scheme based on F plasmids inserted into the FMR-1 gene
B) XX/XO scheme
C) XO/YY scheme
D) hermaphroditic scheme
E) scheme based on single translocations in the X chromosome
Answer: B
Section: 5.2

2) The Lygaeus mode of sex determination is the ________.
A) XY/XX scheme
B) XX/XO scheme
C) XO/YY scheme
D) hermaphroditic scheme
E) scheme based on single translocations in the X chromosome
Answer: A
Section: 5.2

3) The sex of birds, some insects, and other organisms is determined by a ZW chromosomal arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to XY in humans). Assume that a recessive lethal allele on the Z chromosome causes death of an embryo in birds. What sex ratio would result in the offspring if a cross were made between a male heterozygous for the lethal allele and a normal female?
A) 4:1 male to female
B) 2:1 male to female
C) 3:1 male to female
D) 1:2 male to female
E) 1:1 male to female
Answer: B
Section: 5.2

4) A recessive gene for red-green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color-blind) marries a color-blind male. What is the likelihood that this couples first son will be color-blind?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Answer: C
Section: 5.3

5) One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that they will have a daughter with hemophilia? (Note: In this problem, you must include the probability of having a daughter in your computation of the final probability.)
A) 1/16
B) 1/8
C) 1/4
D) 1/2
E) 3/4
Answer: C
Section: 5.3

6) One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that their first son will have hemophilia?
A) 1/16
B) 1/8
C) 1/4
D) 1/2
E) 3/4
Answer: D
Section: 5.3

7) In humans, the genetic basis for determining the sex male is accomplished by the presence of ________.
A) a portion of the Y chromosome
B) one X chromosome
C) a balance between the number of X chromosomes and the number of haploid sets of autosomes
D) high levels of estrogen
E) multiple alleles scattered throughout the autosomes
Answer: A
Section: 5.3

8) Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?
A) 47, XXY
B) 47, 21+
C) 45, X
D) 47, XYY
E) triploidy
Answer: A
Section: 5.3

9) Assume that a man who carries an X-linked gene has children. Assuming normal meiosis and random combination of gametes, the man would pass this gene to ________.
A) half of his daughters
B) all of his daughters
C) all of his sons
D) half of his sons
E) all of his children
Answer: B
Section: 5.3

10) In Drosophila, sex is determined by a balance between the number of haploid sets of autosomes and the number of ________.
A) telomeres
B) centromeres
C) X chromosomes
D) Y chromosomes
E) nucleolar organizers
Answer: C
Section: 5.5

11) For an individual with the XXY chromosomal composition, the expected number of Barr bodies in interphase cells is ________.
A) variable
B) one
C) two
D) three
E) zero
Answer: B
Section: 5.5

12) Assume that you are told that a particular organism, Drosophila, has the XO chromosome complement. You are also told that the autosomal complement is a normal 2n. You know that in humans the XO complement is female determining. Would you be correct in assuming that the Drosophila sex for XO is also female? Choose the answer that includes the correct explanation.
A) Yes, because sex determination in humans and insects is essentially the same.
B) No, sex determination in Drosophila is dependent on the presence or absence of the Y chromosome.
C) No, the chromosomal basis for sex determination in Drosophila is based on the balance between the number of X chromosomes and haploid sets of autosomes.
D) Yes, the presence of an X chromosome determines a female in both organisms.
E) No, it takes two X chromosomes to produce a female in humans and a Y chromosome to produce a male in Drosophila.
Answer: C
Section: 5.6

13) Glucose-6-phosphate dehydrogenase (G6PD) deficiency is inherited as an X-linked recessive gene in humans. A woman whose father suffered from G6PD marries a normal man.

(a) What proportion of their sons is expected to be G6PD?
(b) If the husband were not normal but were G6PD deficient, would you change your answer in part (a)?
Answer:
(a) 1/2
(b) no
Section: 5.3

14) Below is a pedigree of a fairly common human hereditary trait; the boxes represent males and the circles represent females. Filled-in symbols indicate the abnormal phenotype. Given that one gene pair is involved,

(a) Is the inheritance pattern X-linked or autosomal?
(b) Give the genotype of each individual in the pedigree. If more than one genotypic possibility exists, present all possible alternatives.
Answer: (a) autosomal recessive
(b)

Section: 5.3

15) List three abnormalities involving numbers of X chromosomes.
Answer: Klinefelter syndrome, Turner syndrome, XXXX syndrome
Section: 5.3

16) Individuals have been identified who have two different karyotypes, such as 45,X/46,XY or 45,X/46,XX. Such individuals are called ________.
Answer: mosaics
Section: 5.3

17) What particular karyotype was once considered to be related to criminal predisposition?
Answer: XYY
Section: 5.3
18) A small part of the human Y chromosome contains the gene that is responsible for determining maleness. What is the name of this gene?
Answer: SRY (sex-determining region Y)
Section: 5.3

19) Under what condition might a human female have the XY sex chromosome complement?
Answer: This female would have one complete X chromosome and a Y chromosome that lacks SRY.
Section: 5.3

20) A color-blind woman with Turner syndrome (XO) has a father who is color-blind. Given that the gene for the color-blind condition is recessive and X-linked, provide a likely explanation for the origin of the color-blind and cytogenetic conditions in the woman.
Answer: The woman inherited an Xrg chromosome from the father. Nondisjunction in the female (either at meiosis I or II) produced an egg with no X chromosome, which, when fertilized by the Xrg-bearing sperm, produced the Turner syndrome condition.
Section: 5.3

21) Although triple-X human females typically have normal offspring, what kinds of gametes, with respect to the X chromosomes, would you expect from such XXX females? Draw meiotic stages that show the gametes that are expected to be produced.
Answer:

Section: 5.3

22) How many chromosomes do Klinefelter and Turner syndromes have, respectively?
Answer: 47, 45
Section: 5.3

23) Studies done in the 1960s suggested that individuals with the XYY condition were prone to criminal behavior. What conclusions currently seem appropriate concerning this chromosomal condition?
Answer: There is a high, but not constant, correlation between the extra Y chromosome and the predisposition of males to have behavioral problems.
Section: 5.3

24) Describe an experiment in which transgenic mice were used to identify the male-determining region of the Y chromosome.
Answer: When DNA containing only the mouse SRY is injected into normal XX mouse eggs, most of the offspring develop into males.
Section: 5.3
25) Describe three distinct genetic regions of the human Y chromosome.
Answer: PARs = pseudoautosomal regions, NRY = nonrecombining region of the Y, SRY = sex-determining region
Section: 5.3

26) A color-blind, chromatin-positive male child (one Barr body) has a maternal grandfather who was color-blind. The boys mother and father are phenotypically normal. Construct and support (using appropriately labeled diagrams) a rationale whereby the chromosomal and genetic attributes of the chromatin-positive male are fully explained.
Answer: The female (mother) must be heterozygous and undergo nondisjunction at meiosis II to produce the XrgXrgY boy.
Section: 5.5

27) A cross is made between a female calico cat and a male cat having the gene for black fur on his X chromosome. What fraction of the offspring would one expect to be calico?
Answer: 1/4
Section: 5.5

28) Dosage compensation leads to a variety of interesting coat color patterns in certain mammals. For instance, a female cat that is heterozygous for two coat color alleles, say black and orange, will usually have the calico or mosaic phenotype. Describe the chromosomal basis for the mosaicism (calico) in the female. Explain why chromosomally normal male cats do not show the mosaic phenotype, but XXY male cats can be calico.
Answer: Because of dosage compensation, one of the X chromosomes randomly turns off early in development. Once such a chromosome is inactivated, it remains so in daughter cells. Recessive alleles on the remaining active X chromosome are expressed because their normal allele (on the inactive X chromosome) is not capable of expression. Because males typically have only one X chromosome, X chromosome inactivation does not occur; however, in XXY males that are heterozygous for certain coat color genes, such inactivation and mosaicism are possible.
Section: 5.5

29) How many Barr bodies would one expect to see in cells of Turner syndrome females and Klinefelter syndrome males?
Answer: zero and one, respectively
Section: 5.5

30) What can cause phenotypic mosaicism for X-linked genes in female mammals?
Answer: dosage compensation involving the X chromosome
Section: 5.5

31) Dosage compensation in mammals typically involves the random inactivation of one of the two X chromosomes relatively early in development. Such X chromosome inactivation often leads to phenotypic mosaicism. Assume that black fur in cats is due to the X-linked recessive gene b, whereas its dominant allele B produces yellow fur. A Bb heterozygote is a mosaic called tortoise shell or calico. Using appropriate gene symbols, diagram a mating between a black male and a calico female. Give the phenotypes and genotypes of all the offspring.
Answer:
bY X Bb =
Bb (calico female), bb (black female), BY (yellow male), bY (black male)
Section: 5.5
32) What is the composition of a Barr body?
Answer: X chromosomeassociated proteins
Section: 5.5

33) Give the sex-chromosome constitution (X and Y chromosomes) and possible genotypes of offspring resulting from a cross between a white-eyed female (Xw XwY) and a wild-type male (normal chromosome complement) in Drosophila melanogaster. Include all zygotic combinations whether viable or unviable.
Answer:
X+XwXw = unviable (dies at third instar stage)
XwXwY = white-eyed female
X+Y = wild-type male
YY = unviable (dies at egg stage)
X+XwY = wild-type female
XwYY = white-eyed male
X+Xw = wild-type female
XwY = white-eyed male
Section: 5.6

34) In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The females father had red eyes, and the mother had white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.
Answer: Nondisjunction could have occurred either at meiosis I or meiosis II in the mother, thus giving the XwXwY complement in the offspring.
Section: 5.6

35) In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The females mother and father had red eyes. The mother, however, was heterozygous for the gene for white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.
Answer: Nondisjunction would have occurred at meiosis II in the mother, thus giving the XwXwY complement in the offspring.
Section: 5.6
36) Give the sex of the following organisms assuming that the autosomes are present in the normal number.

Sex Chromosome Organism
Complement Humans Drosophila

XX ________ ________
XY ________ ________
XO ________ ________
XXX ________ ________
XXY ________ ________
Answer:
Sex Chromosome Organism
Complement Humans Drosophila
XX female female
XY male male
XO female male
XXX female female
XXY male female
Section: 5.6

37) Assuming a normal number of autosomes, what would be the sex of the following: XXY mouse, XXY Drosophila?
Answer: male and female, respectively
Section: 5.6

38) Data produced by C. Bridges in the early part of this century indicate that sex in Drosophila is determined by ________.
Answer: a balance between the number of X chromosomes and the number of haploid sets of autosomes
Section: 5.6

39) In Drosophila, the sex of a fly with the karyotype XO:2A is ________.
Answer: male
Section: 5.6

40) In humans, the male is the homogametic sex.
Answer: FALSE
Section: 5.2

41) Normally in humans, all the sons of a male showing a sex-linked phenotype will inherit the trait.
Answer: FALSE
Section: 5.3

42) Normally in humans, all the sons of a female homozygous for a sex-linked recessive gene will inherit that trait.
Answer: TRUE
Section: 5.3
43) Sex-influenced genes cause males to be males and females to be females.
Answer: FALSE
Section: 5.3

44) Sex-limited genes cause males to be males and females to be females.
Answer: FALSE
Section: 5.3

45) An individual with Klinefelter syndrome generally has one Barr body.
Answer: TRUE
Section: 5.3

46) An individual with Turner syndrome has no Barr bodies.
Answer: TRUE
Section: 5.5

47) A typical XX human female has one Barr body.
Answer: TRUE
Section: 5.5

48) Dosage compensation is accomplished in humans by inactivation of the Y chromosome.
Answer: FALSE
Section: 5.5

49) In Drosophila, the female is the heterogametic sex.
Answer: FALSE
Section: 5.6

50) In Drosophila melanogaster, sex is determined by the ratio of the number of X chromosomes to the number of haploid sets of autosomes.
Answer: TRUE
Section: 5.6

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